This proposal is a continuation of our research on the mechanisms of broad sensitization, particularly regarding the effects of blood transfusions after transplant rejection. Our previous results are the subject of 11 papers, 8 published and 3 in press. We now propose to study the rate of HLA antibody synthesis in broadly sensitized patients and its inhibition by different immunosuppressive agents. Our objectives are to develop effective protocols to inhibit anti-HLA antibody synthesis, to minimize the risk of toxicity of such protocols, and to identify the patients who may benefit the most, so that transplantation could be considered as a viable option despite the presence of broadly reactive antibodies. The study contemplates perturbing the system by means of a plasma exchange, which will induce, first, an artificial drop of antibody concentration, and second, a rebound to its original levels. This rebound can be used as an indication of the rate of antibody synthesis in a given patient and it will be measured by rigorously quantitative techniques. Subsequent plasma exchanges performed under different conditions of immunosuppression will allow to determine the effectiveness of the drug protocols using the patient as its own control- If the patients need to be transfused during the study period, cryopreserved, HLA matched blood will be given to minimize the immunogenicity of blood transfusions. With this design we will find out, after a 4-6 week period, whether the antibody levels in a specific patient are refractory or sensitive to the immunosuppression utilized, and the factors that are associated with, and could be predictive of, one or the other outcome. In contrast to previous trials, the patients will be considered for transplantation only if the antibody synthesis is clearly suppressed. In this revised application, preliminary results on 3 patients evaluated after plasma exchanges and immunosuppression are presented. The results demonstrate the feasibility of the studies proposed. They also suggest the possibility of successful use of plasma exchanges without immunosuppression, a fact that, if confirmed, could lead to a wide utilization of this procedure.